Conductive paste, preparation method and application thereof

Abstract

This application provides a conductive paste that, by introducing inexpensive metals such as nickel and aluminum into the paste, increases the proportion of conductive metals other than silver to a maximum of 50%, significantly reducing the amount of precious silver used, effectively controlling material costs, and alleviating cost pressures caused by soaring silver prices. By controlling the particle size distribution of conductive metals other than silver (D50 is 2-9μm, D100 < 30μm), the paste is ensured to have good permeability and formability during screen printing, without screen clogging or broken grid lines, forming complete and uniform fine grid lines, laying the foundation for high efficiency.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic technology, specifically relating to a conductive paste, particularly a conductive paste with low silver content, as well as a method for preparing the conductive paste and its application in solar cells. Background Technology

[0002] A solar cell is a semiconductor device that converts light energy into electrical energy. Its core lies in forming electrodes on the surface of a silicon wafer using a conductive metal paste to collect and extract photogenerated charge carriers. The conductive paste is typically applied to the front and back of the silicon wafer using a screen printing process. After drying and sintering, it forms fine grid lines and main grid lines. The fine grid lines are responsible for collecting current, while the main grid lines are used to converge the current and connect the cells in series. Currently, silver paste has become the mainstream material for solar cell electrode manufacturing due to its excellent conductivity and solderability.

[0003] In existing technologies, to achieve good ohmic contact and reliable conductivity, the mass ratio of silver powder in conductive pastes is typically as high as 90%. However, as a precious metal, the price of silver fluctuates dramatically due to market supply and demand. In recent years, the price of silver has continued to rise. Taking photovoltaic silver powder as an example, its price was approximately 4,700 yuan / kg in 2020, rising to 6,500 yuan / kg in 2024. In 2025, driven by the overall upward trend in silver prices, the price of silver powder even exceeded 15,000 yuan / kg, approaching 20,000 yuan / kg. The continuous rise in silver prices has led to a sharp increase in the proportion of silver paste cost in the total cost of batteries, putting enormous cost pressure on mainstream TOPCon, HJT, and BC batteries.

[0004] The high cost of silver paste has become a key factor restricting the further development of the solar cell industry. Although theoretically some silver can be replaced by reducing the amount of silver powder or introducing other inexpensive metals, simple substitution often leads to problems such as decreased electrode printing performance (e.g., grid blockage, broken grids), increased contact resistance, and insufficient adhesion after sintering, which in turn causes fluctuations in cell conversion efficiency or even reliability failure.

[0005] Therefore, how to significantly reduce the silver content while ensuring the stability of battery conversion efficiency and long-term reliability has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned problems existing in the prior art, and provides a conductive paste with low silver content, low cost, and high conversion efficiency and high reliability of battery, as well as its preparation method and application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] One of the objectives of this application is to provide a conductive paste, comprising conductive metal powder and an organic mixture;

[0009] The conductive metal powder includes silver powder and / or silver-coated powder, as well as conductive metals other than silver;

[0010] The conductive metal other than silver is selected from one or more of nickel, aluminum, copper, tungsten, and tin, and its weight percentage in the conductive paste is 1-50%.

[0011] The specific surface area of ​​the conductive metal other than silver is 0.1-0.5 m² / g, and its particle shape is spherical, near-spherical, irregularly shaped spherical, or amorphous.

[0012] The particle size distribution of the conductive metal other than silver satisfies D50 of 2-9 μm and D100 of less than 30 μm.

[0013] In some embodiments, the specific surface area of ​​the conductive metal other than silver is 0.1-0.45 m² / g.

[0014] In some embodiments, the D50 of the conductive metal other than silver is 3.5-8.0 μm.

[0015] In some embodiments, the conductive metal other than silver is a powder prepared by physical vapor deposition or a chemical method.

[0016] In some embodiments, the conductive metal other than silver exists in the form of an elemental metal, a metal compound, a metal alloy, or a silver-coated metal.

[0017] In some embodiments, the conductive metal powder further includes separate silver powder with a particle size distribution D50 of 1.6-1.8 μm and a specific surface area of ​​0.4-0.45 m² / g.

[0018] In some embodiments, the conductive metal other than silver accounts for 9-80% by weight in the conductive paste.

[0019] In some embodiments, the conductive paste contains no more than 70% silver-coated base metal powder, no less than 40% silver, and no more than 50% base metal.

[0020] A second objective of this application is to provide a method for preparing the conductive paste as described above, comprising the following steps:

[0021] The conductive metal powder of the formula amount is premixed with the organic mixture to obtain a premix;

[0022] The premix is ​​rolled to obtain the conductive slurry.

[0023] In some embodiments, the premixing is performed using a dual planetary mixer, and the rolling is performed using a three-roll mill.

[0024] A third objective of this application is to provide a solar cell, wherein the grid electrodes of the solar cell are formed by printing and sintering the conductive paste as described above.

[0025] In some embodiments, the solar cell is a TOPCon cell, and its back side includes a passivated contact structure consisting of an interface oxide layer and a doped polycrystalline silicon layer.

[0026] In some embodiments, the grid line electrode includes a positive electrode grid located on the front side of the battery and / or a negative electrode grid located on the back side of the battery; the sintering temperature is 300-760°C; the grid line electrode is printed by single-layer printing or by double-layer printing, which involves first printing a pure silver paste base layer and then printing the conductive paste.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The conductive paste provided in this application introduces inexpensive metals such as nickel and aluminum into the paste, increasing the proportion of conductive metals other than silver to a maximum of 50%, which significantly reduces the amount of precious metal silver used, effectively controls material costs, and alleviates the cost pressure brought about by the high price of silver. By controlling the particle size distribution of conductive metals other than silver (D50 is 2-9μm, D100 < 30μm), the paste is ensured to have good permeability and formability during screen printing, without screen clogging or broken grid lines, forming complete and uniform fine grid lines, laying the foundation for high efficiency.

[0029] The conductive paste provided in this application, by controlling the specific surface area (0.1-0.5 m² / g), enables the base metal powder to form a dense conductive network with the silver powder during sintering, and also to form a low-resistance ohmic contact with the silicon substrate, thus avoiding efficiency loss caused by excessive contact resistance.

[0030] The conductive paste provided in this application is compatible with both high-temperature sintering (760°C) and low-temperature inert gas sintering (300°C) processes. It can be used in conventional batteries and is also perfectly suited for temperature-sensitive high-efficiency battery structures such as TOPCon, ensuring high performance under different technical approaches. In the embodiments, the battery conversion efficiency reaches over 26.55%, comparable to pure silver paste.

[0031] The conductive paste provided in this application adopts a silver-clad metal form (such as silver-clad nickel or silver-clad aluminum), using an outer silver shell to prevent the internal base metal from oxidizing during storage and sintering, thus ensuring the long-term conductivity stability of the electrode.

[0032] The conductive paste provided in this application, through particle size control (D100 < 30 μm), eliminates physical damage to the silicon substrate or fragile passivation layer caused by coarse particles. The low-temperature sintering process protects the tunneling oxide layer and polycrystalline silicon layer on the back of the TOPCon cell from damage, ensuring the integrity and long-term reliability of the passivation structure. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the solar cell structure provided in Embodiment 1 of the present invention.

[0035] Figure 2 This is a schematic diagram of the solar cell structure provided in Embodiment 2 of the present invention.

[0036] Figure 3 This is a schematic diagram of the solar cell structure provided in Embodiment 3 of the present invention.

[0037] Figure 4 This is a schematic diagram of the solar cell structure provided in Embodiment 4 of the present invention. Detailed Implementation

[0038] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0039] In the description of this application, it should be understood that the terms "upper", "lower", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0041] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments.

[0042] One of the objectives of this application is to provide a conductive paste, comprising conductive metal powder and an organic mixture;

[0043] The conductive metal powder includes silver powder and / or silver-coated powder, as well as conductive metals other than silver; the conductive metals other than silver are selected from one or more of nickel, aluminum, copper, tungsten, and tin, and their weight percentage in the conductive slurry is 1-50%; the specific surface area of ​​the conductive metals other than silver is 0.1-0.5 m² / g, and their particle shape is spherical, near-spherical, irregularly shaped spherical, or amorphous; the particle size distribution of the conductive metals other than silver satisfies D50 of 2-9 μm and D100 of less than 30 μm.

[0044] It is understandable that conductive metals other than silver are selected from one or more of nickel, aluminum, copper, tungsten, and tin, and their weight percentage in the paste is 1-50%. Introducing metals such as nickel and aluminum, whose prices are much lower than silver (nickel is about 1 / 100 the price of silver, and aluminum is about 1 / 200 the price of silver), can replace some of the silver powder. A substitution rate of up to 80% can significantly reduce the amount of precious metals used, thus lowering costs.

[0045] Furthermore, in this embodiment, the D50 of conductive metals other than silver is 2-9 μm, and the D100 is <30 μm. This avoids the problems caused by excessively coarse particles (D50>9 μm or D100>30 μm), which can easily lead to screen blockage and grid breakage; and excessively fine particles (D50<2 μm), which can easily agglomerate and result in poor printing consistency. This invention ensures good permeability and formability of the paste through particle size control. In addition, because solar cell silicon wafers are thin and have fragile PN junctions or passivation layers on their surface, large particles larger than 30 μm may pierce the silicon wafer, damage the passivation layer, or cause PN junction leakage after printing or sintering.

[0046] In this embodiment, conductive metals other than silver are used, and their particle shapes are spherical, near-spherical, irregularly shaped spherical, or amorphous. Spherical or near-spherical particles have good fluidity in the organic carrier and are not easy to settle, which ensures the long-term reliability of the slurry's storage stability and printing consistency.

[0047] Furthermore, in this embodiment, the specific surface area of ​​the conductive metal other than silver is 0.1-0.5 m² / g, preferably 0.1-0.45 m² / g, because the specific surface area directly affects the sintering activity. Too high a specific surface area (>0.5 m² / g) can easily lead to over-burning, damaging the PN junction or causing blistering; too low a specific surface area (<0.1 m² / g) results in insufficient sintering and high contact resistance. This invention ensures that the base metal powder can bond well with the silver powder during sintering, forming a low-resistance ohmic contact with the silicon substrate by controlling the specific surface area.

[0048] In some embodiments, the D50 of the conductive metal other than silver is 3.5-8.0 μm.

[0049] It is understandable that this range directly corresponds to the measured D50 values ​​of all base metal powders (nickel powder 3.5-4.5μm, aluminum powder 7.0-8.0μm, silver-coated nickel powder 3.6-4.2μm), and is the experimentally verified optimal range, ensuring the best balance between printability and sinterability.

[0050] In some embodiments, the conductive metal other than silver is a powder prepared by physical vapor deposition or a chemical method.

[0051] It is understandable that conductive metals other than silver are prepared by PVD or chemical methods. Metal powders prepared by PVD or chemical methods have high purity and low impurity content, which avoids electrode corrosion or performance degradation caused by impurities (such as Fe, Cu, etc.) and improves the long-term reliability of the battery.

[0052] In some embodiments, the conductive metal other than silver exists in the form of an elemental metal, a metal compound, a metal alloy, or a silver-coated metal.

[0053] It is understandable that base metals such as aluminum and nickel are easily oxidized in air, forming a non-conductive oxide layer that leads to electrode failure. The silver-clad structure isolates the base metal core from the outside environment, and the outer silver layer melts and connects during sintering, forming a continuous conductive path. In addition, silver-clad structures (such as silver-clad nickel and silver-clad aluminum) use inexpensive metals as the core and only coat a thin layer of silver on the outside, which not only ensures the continuity and conductivity during sintering, but also significantly reduces the amount of silver used, achieving a synergistic optimization of cost and performance.

[0054] In some embodiments, the conductive metal powder further includes separate silver powder with a particle size distribution D50 of 1.6-1.8 μm and a specific surface area of ​​0.4-0.45 m² / g.

[0055] It is understandable that finer silver powder (1.6μm) has higher sintering activity. During the sintering process, it melts first, wets and connects with coarser base metal powder (3.5-8.0μm), forming a dense conductive network to compensate for the fact that the conductivity of base metal is slightly inferior to that of pure silver.

[0056] In some embodiments, the conductive metal other than silver accounts for 9-80% by weight in the conductive paste.

[0057] It is understandable that the content of the substitute metals will be further limited to 9-50% to ensure feasibility while significantly reducing silver content.

[0058] In some embodiments, the silver-coated base metal powder content is not more than 70%, the silver content is not less than 40%, and the base metal content is not more than 50% in the total powder amount.

[0059] It is understood that this embodiment provides multiple silver-coating formulation modes: ① independent silver powder + base metal element; ② silver-coated powder + a small amount of silver powder; ③ pure silver-coated powder. Among them, in the pure silver-coated powder formulation, the base metal accounts for up to 50%, which greatly reduces material costs.

[0060] The conductive paste provided in this application introduces inexpensive metals such as nickel and aluminum into the paste, increasing the proportion of conductive metals other than silver to a maximum of 50%, which significantly reduces the amount of precious metal silver used, effectively controls material costs, and alleviates the cost pressure brought about by the high price of silver. By controlling the particle size distribution of conductive metals other than silver (D50 is 2-9μm, D100 < 30μm), the paste is ensured to have good permeability and formability during screen printing, without screen clogging or broken grid lines, forming complete and uniform fine grid lines, laying the foundation for high efficiency.

[0061] The conductive paste provided in this application, by controlling the specific surface area (0.1-0.5 m² / g), enables the base metal powder to form a dense conductive network with the silver powder during sintering, and also to form a low-resistance ohmic contact with the silicon substrate, thus avoiding efficiency loss caused by excessive contact resistance.

[0062] The conductive paste provided in this application is compatible with both high-temperature sintering (760°C) and low-temperature inert gas sintering (300°C) processes. It can be used in conventional batteries and is also perfectly suited for temperature-sensitive high-efficiency battery structures such as TOPCon, ensuring high performance under different technical approaches. In the embodiments, the battery conversion efficiency reaches over 26.55%, comparable to pure silver paste.

[0063] The conductive paste provided in this application adopts a silver-clad metal form (such as silver-clad nickel or silver-clad aluminum), using an outer silver shell to prevent the internal base metal from oxidizing during storage and sintering, thus ensuring the long-term conductivity stability of the electrode.

[0064] The conductive paste provided in this application, through particle size control (D100 < 30 μm), eliminates physical damage to the silicon substrate or fragile passivation layer caused by coarse particles. The low-temperature sintering process protects the tunneling oxide layer and polycrystalline silicon layer on the back of the TOPCon cell from damage, ensuring the integrity and long-term reliability of the passivation structure.

[0065] A second objective of this application is to provide a method for preparing the conductive paste as described above, comprising the following steps:

[0066] The conductive metal powder of the formula amount is premixed with the organic mixture to obtain a premix;

[0067] The premix is ​​rolled to obtain the conductive slurry.

[0068] In some embodiments, the premixing is performed using a dual planetary mixer, and the rolling is performed using a three-roll mill.

[0069] The conductive paste preparation process provided in this application is simple. By introducing inexpensive metals such as nickel and aluminum into the paste, the proportion of conductive metals other than silver is increased to a maximum of 80%, which significantly reduces the amount of precious metal silver used, effectively controls material costs, and alleviates the cost pressure brought about by the high price of silver. By controlling the particle size distribution of conductive metals other than silver (D50 is 2-9μm, D100 < 30μm), the paste is ensured to have good permeability and formability during screen printing, without screen clogging or broken grids, forming complete and uniform fine grid lines, laying the foundation for high efficiency.

[0070] A third objective of this application is to provide a solar cell, wherein the grid electrodes of the solar cell are formed by printing and sintering the conductive paste as described above.

[0071] In some embodiments, the solar cell is a TOPCon cell, and its back side includes a passivated contact structure consisting of an interface oxide layer and a doped polycrystalline silicon layer.

[0072] It is understood that this embodiment is adapted to a high-efficiency battery structure to ensure passivation reliability. The ultra-thin tunneling oxide layer and polycrystalline silicon layer on the back of the TOPCon battery are sensitive to high temperatures, and high-temperature sintering can easily damage their passivation effect. The slurry of this invention is suitable for low-temperature sintering, protecting this core structure.

[0073] In some embodiments, the grid line electrode includes a positive electrode grid located on the front side of the battery and / or a negative electrode grid located on the back side of the battery; the sintering temperature is 300-760°C; the grid line electrode is printed by single-layer printing or by double-layer printing, which involves first printing a pure silver paste base layer and then printing the conductive paste.

[0074] It is understandable that this invention is compatible with different sintering windows. High-temperature sintering (760℃) is suitable for conventional batteries and electrodes that need to penetrate the front passivation layer, ensuring good ohmic contact with the P+ layer. Low-temperature sintering (300℃) is suitable for temperature-sensitive high-efficiency batteries such as TOPCon, protecting the back passivation contact structure from damage, while the silver coating structure ensures that the base metal does not oxidize at low temperatures. This temperature range allows the slurry of this invention to be adapted to various battery structures and process routes, all achieving high efficiency.

[0075] In addition, this embodiment adopts a two-layer printing method. For formulations with extremely low silver content, a layer of pure silver paste is first printed as the bottom layer to ensure good ohmic contact with the silicon substrate. The low silver paste is then printed on the top layer, which reduces costs and maintains efficiency. For formulations with moderate base metal content, single-layer printing can be used directly to simplify the process.

[0076] The conductive paste provided in this application forms the grid electrodes of a solar cell after printing and sintering. By introducing inexpensive metals such as nickel and aluminum into the paste, the proportion of conductive metals other than silver is increased to a maximum of 80%, which significantly reduces the amount of precious silver used, effectively controls material costs, and alleviates the cost pressure caused by the high price of silver. By controlling the particle size distribution of conductive metals other than silver (D50 is 2-9μm, D100 < 30μm), the paste is ensured to have good permeability and formability during screen printing, without screen blockage or broken grids, forming complete and uniform fine grid lines, laying the foundation for high efficiency.

[0077] To further understand the present invention, the present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited to the following embodiments.

[0078] Example 1

[0079] This embodiment provides a conductive paste comprising the following components by weight percentage: 79 parts silver powder, 2 parts glass powder, 10 parts organic mixture, and 9 parts nickel powder. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0080] The silver powder has a median particle size D50 of 1.6 μm and a specific surface area of ​​0.45 m² / g; the nickel powder has a D50 of 3.5 μm, a D100 of 20 μm, and a specific surface area of ​​0.45 m² / g.

[0081] The cells are screen-printed onto silicon wafers using a 500-mesh, 15-aperture screen, without any screen blockages, missing or broken grids, and then sintered at 760°C, resulting in a cell conversion efficiency of 26.65%.

[0082] Figure 1 This is a schematic diagram of the solar cell structure provided in Embodiment 1 of the present invention. As shown in the figure, the solar cell is a bifacial cell structure, including: a silicon substrate (marked "P" in the figure): serving as the main semiconductor material of the cell, used for the generation and separation of photogenerated carriers; a back passivation film: located on the back of the silicon substrate, used to reduce the carrier recombination rate and improve the cell efficiency; a passivation and antireflection film: located on the front of the silicon substrate, serving the dual functions of passivating surface defects and reducing incident light reflection; a negative electrode grid: located on the back of the cell, used to collect and export electrons; and a positive electrode grid: located on the front of the cell, used to collect and export holes. The positive electrode grid and / or the negative electrode grid are formed by printing and sintering the paste described in the aforementioned conductive paste embodiment.

[0083] In this embodiment, inexpensive nickel powder is used to replace part of the silver powder, reducing the silver content (by solids) to approximately 88.8%, thus lowering the slurry cost. By controlling the nickel powder particle size (D50=3.5μm, D100<30μm) and specific surface area (0.45 m² / g), excellent printability and sintering activity of the slurry are ensured, forming a good conductive network with the silver powder. The conversion efficiency reaches 26.65%, and there are no printing defects, guaranteeing the reliability and stability of the battery.

[0084] Example 2

[0085] This embodiment provides a conductive paste comprising the following components by weight percentage: 70 parts silver powder, 2 parts glass powder, 10 parts organic mixture, and 18 parts nickel powder. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0086] The silver powder has a median particle size D50 of 1.6 μm and a specific surface area of ​​0.45 m² / g; the nickel powder has a D50 of 4.5 μm, a D100 of 25 μm, and a specific surface area of ​​0.36 m² / g.

[0087] The cells are screen-printed onto silicon wafers using a 500-mesh, 15-aperture screen, without any screen blockages, missing or broken grids, and then sintered at 760°C, resulting in a cell conversion efficiency of 26.56%.

[0088] Figure 2 This is a schematic diagram of the solar cell structure provided in Embodiment 2 of the present invention. As shown in the figure, the solar cell is a TOPCon (tunneling oxide passivated contact) or bifacial cell structure based on an n-type silicon substrate, including: n-type silicon substrate (marked "n" in the figure): As the main material of the battery, it is a phosphorus-doped n-type silicon wafer used for the generation and separation of photogenerated carriers; Front doped layer (P+ layer): Located on the front side of the silicon substrate, it is a boron-doped emitter used to establish an internal electric field and collect holes; Passivation and antireflection film: Located above the front doped layer, it has the dual function of passivating surface defects and reducing incident light reflection, and is usually silicon oxide, silicon nitride or a stack thereof; Back passivation film: Located on the back side of the silicon substrate, it is used to reduce the recombination rate of carriers on the back surface; Tunneling oxide / polycrystalline silicon layer (n+ layer): Located between the back passivation film and the silicon substrate (or directly on the back side of the silicon substrate), it consists of an ultrathin silicon oxide layer and a doped polycrystalline silicon layer, realizing selective transport of carriers; Negative electrode fine grid: Located on the back side of the battery, in contact with the back polycrystalline silicon layer, it is used to collect and export electrons; Positive electrode fine grid: Located on the front side of the battery, it penetrates the passivation and antireflection film and contacts the P+ layer, it is used to collect and export holes. The positive electrode fine grid and / or negative electrode fine grid are formed by printing and sintering the paste described in the aforementioned conductive paste embodiment.

[0089] In this embodiment, the amount of nickel powder is further increased to 18 parts, and the silver content (solid content) is reduced to approximately 79.5%, significantly reducing the amount of precious metals used. The nickel powder has a specific surface area of ​​0.36 m² / g and can still maintain moderate activity under high-temperature sintering. It matches well with silver powder, and the efficiency fluctuates only slightly (26.56%). There are no printing abnormalities, proving that battery performance and reliability can still be guaranteed even with a large-scale substitution.

[0090] Example 3

[0091] This embodiment provides a conductive paste comprising the following components by weight percentage: 10 parts silver powder, 70 parts silver-coated nickel powder (silver content 40%), and 10 parts organic mixture. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0092] The silver powder has a median particle size D50 of 1.8 μm and a specific surface area of ​​0.4 m² / g; the silver-coated nickel powder has a D50 of 3.6 μm, a D100 of 28 μm, and a specific surface area of ​​0.36 m² / g.

[0093] First, a layer of pure silver paste is printed and sintered on a silicon wafer. Then, the silver-nickel paste is printed through a 500-mesh, 20-aperture screen and sintered in an inert gas atmosphere at 300°C. There are no screen blockages, no false printing, and no broken grids. The resulting battery has a conversion efficiency of 26.55%.

[0094] Figure 3 This is a schematic diagram of a solar cell structure provided in an embodiment of the present invention, specifically a TOPCon (tunneling oxide passivated contact) cell structure. As shown in the figure, the solar cell includes: an n-type silicon substrate: serving as the main material of the cell, used for the generation and separation of photogenerated carriers; a front doped layer (P+ layer): located on the front side of the silicon substrate, serving as the emitter formed by boron doping, used to establish an internal electric field and collect holes; a passivation and antireflection film: located above the front doped layer, serving the dual functions of passivating surface defects and reducing incident light reflection; and a back passivation tunneling layer: located on the back side of the silicon substrate, consisting of an ultrathin tunneling oxide layer (P+ layer). ) and doped polycrystalline silicon layer ( The battery consists of: a back passivation film, located above the back passivation tunneling layer, which further reduces back surface recombination and is typically a dielectric film such as silicon nitride; a positive electrode grid, located on the front side of the battery, which penetrates the passivation antireflection film and contacts the P+ layer to collect and export holes; and a negative electrode grid, located on the back side of the battery, which penetrates the back passivation film and contacts the back passivation tunneling layer (specifically an n+ polycrystalline silicon layer) to collect and export electrons. The positive and / or negative electrode grids are formed by printing and sintering the paste described in the aforementioned conductive paste embodiment. By introducing inexpensive metals such as nickel and aluminum (1-80%) into the positive and / or negative electrode pastes, the amount of precious metal silver used is significantly reduced (in the examples, the silver content can be as low as 15%), directly reducing the battery manufacturing cost.

[0095] This embodiment uses silver-coated nickel powder, with inexpensive nickel as the core and only 15% silver coating, reducing the total silver content (solids) to approximately 24.4%, significantly lowering costs. The silver coating prevents nickel oxidation, and inert gas sintering ensures conductivity; the underlying pure silver paste guarantees ohmic contact. The particle size distribution is reasonable, printing is excellent, and efficiency reaches 26.55%, balancing cost reduction and reliability.

[0096] Example 4

[0097] This embodiment provides a conductive paste comprising the following components by weight percentage: 60 parts of silver-coated nickel powder (50% silver content) and 10 parts of an organic mixture. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0098] The silver-coated nickel powder has a D50 of 4.2 μm, a D100 of 20 μm, and a specific surface area of ​​0.3 m² / g.

[0099] First, a layer of pure silver paste is printed and sintered on a silicon wafer. Then, the silver-nickel paste is printed through a 500-mesh, 20-aperture screen and sintered in an inert gas atmosphere at 300°C. There are no screen blockages, no false printing, and no broken grids. The resulting battery has a conversion efficiency of 26.6%.

[0100] Figure 4 This is a schematic diagram of a high-efficiency solar cell structure according to an embodiment of the present invention, specifically a detailed structural diagram of a TOPCon (tunneling oxide passivated contact) cell. As shown in the figure, the cell uses an n-type silicon wafer as a substrate and employs a front boron-diffused emitter and a back tunneling oxide passivated contact structure, specifically including: - Fine grid: Located on the outermost side of the battery, it is the positive electrode grid line formed by printing and sintering the low silver conductive paste described in this invention, used to collect holes. (Silicon nitride) layer: located in Above the layer, it acts as an anti-reflection layer, reducing the reflection of incident light and also having a certain passivation effect. (Alumina) layer: located in Layers and Between the layers, as a passivation layer, for The emitter surface provides excellent field-effect passivation, reducing carrier recombination. Layer: Located on the front side of the silicon substrate, it is the emitter formed by boron doping and constitutes part of the pn junction. n: refers to the n-type silicon substrate. - Fine grid: Located on the outermost side of the back of the battery, it is the back electrode grid line formed by printing and sintering the low silver conductive paste described in this invention, and is used to collect electrons. (Silicon nitride) layer: located in On the outer side of the layer, it serves as a back passivation film, protecting the back structure and further passivating it. Layer: i.e. The n-type doped polycrystalline silicon layer, together with the interface oxide, forms a passivated contact structure, enabling selective transport of charge carriers. Between the layers is an ultrathin tunneling oxide layer ( This allows majority carriers (electrons) to tunnel through while blocking minority carriers (holes), achieving excellent passivated contacts. n: refers to an n-type silicon substrate.

[0101] This embodiment does not add any independent silver powder; the entire conductive phase is silver-coated nickel powder, with a total silver content (solids) of only 15% and base metal nickel accounting for 85%, greatly reducing material costs. The silver-coated nickel powder has a D50 of 4.2 μm and a specific surface area of ​​0.3 m² / g, resulting in smooth printing and forming a continuous conductive channel after sintering, achieving an efficiency of 26.6%. This demonstrates that high efficiency and reliability can be maintained even with extremely low silver content.

[0102] Example 5

[0103] This embodiment provides a conductive paste comprising the following components by weight percentage: 70 parts of silver-coated aluminum powder (60% silver content) and 10 parts of an organic mixture. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0104] The silver-coated aluminum powder has a D50 of 9.0 μm, a D100 of 28 μm, and a specific surface area of ​​0.15 m² / g.

[0105] First, a layer of pure silver paste is printed and sintered on a silicon wafer. Then, the silver-aluminum paste is printed through a 325-mesh 80-aperture screen and sintered in an inert gas atmosphere at 300°C. There are no screen blockages, no false printing, and no broken grids. The resulting battery has a conversion efficiency of 26.62%.

[0106] This embodiment uses silver-coated aluminum powder, as aluminum is much cheaper than nickel, further reducing costs. The aluminum powder has a D50 of 7.0 μm and a specific surface area of ​​0.15 m² / g. The relatively coarse particles, combined with low-temperature inert gas sintering, prevent aluminum oxidation, while the silver layer ensures adhesion. It exhibits good printability and an efficiency of 26.62%, demonstrating the feasibility and reliability of aluminum as a substitute metal.

[0107] Example 6

[0108] This embodiment provides a conductive paste comprising the following components by weight percentage: 50 parts of silver-coated aluminum powder (50% silver content) and 10 parts of an organic mixture. The paste is premixed using a dual planetary mixer and then rolled using a three-roll mill to obtain the conductive paste.

[0109] The silver-coated aluminum powder has a D50 of 8.0 μm, a D100 of 28 μm, and a specific surface area of ​​0.1 m² / g.

[0110] First, a layer of pure silver paste is printed and sintered on a silicon wafer. Then, the silver-aluminum paste is printed through a 325-mesh 80-aperture screen and sintered in an inert gas atmosphere at 300°C. There are no screen blockages, no false printing, and no broken grids. The resulting battery has a conversion efficiency of 26.65%.

[0111] In this embodiment, the silver content in the silver-coated aluminum powder is adjusted to 20%, while the aluminum content remains at 80%, maintaining a low-cost advantage. The aluminum powder has a D50 of 8.0 μm and a specific surface area of ​​0.1 m² / g, exhibiting suitable sintering activity and good compatibility with the underlying pure silver paste, achieving an efficiency of 26.65%, comparable to pure silver paste. By optimizing the particle size and coating structure, a highly reliable silver reduction solution has been achieved.

[0112] The above are merely preferred embodiments of this application, and only specifically describe the technical principles of this application. These descriptions are only for explaining the principles of this application and should not be construed as limiting the scope of protection of this application in any way. Based on this explanation, any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, as well as other specific embodiments of this application that can be conceived by those skilled in the art without creative effort, should be included within the scope of protection of this application.

Claims

1. A conductive paste, characterized in that, Includes conductive metal powder and organic mixtures; The conductive metal powder includes silver powder and / or silver-coated powder, as well as conductive metals other than silver; The conductive metal other than silver is selected from one or more of nickel, aluminum, copper, tungsten, and tin, and its weight percentage in the conductive paste is 1-50%. The specific surface area of ​​the conductive metal other than silver is 0.1-0.5 m² / g, and its particle shape is spherical, near-spherical, irregularly shaped spherical, or amorphous. The particle size distribution of the conductive metal other than silver satisfies D50 of 2-9 μm and D100 of less than 30 μm.

2. The conductive paste according to claim 1, characterized in that, The specific surface area of ​​the conductive metal other than silver is 0.1-0.45 m² / g.

3. The conductive paste according to claim 1, characterized in that, The D50 of the conductive metal other than silver is 3.5-8.0 μm.

4. The conductive paste according to claim 1, characterized in that, The conductive metal other than silver is a powder prepared by physical vapor deposition or chemical methods.

5. The conductive paste according to claim 1, characterized in that, The conductive metal other than silver exists in the form of elemental metal, metal compound, metal alloy, or silver-coated metal.

6. The conductive paste according to claim 1, characterized in that, The conductive metal powder also includes separate silver powder, the silver powder having a particle size distribution D50 of 1.6-1.8 μm and a specific surface area of ​​0.4-0.45 m² / g.

7. The conductive paste according to claim 1, characterized in that, The weight percentage of the conductive metal other than silver in the conductive paste is 9-50%.

8. The conductive paste according to any one of claims 1-7, characterized in that, The conductive paste contains no more than 70% silver-coated base metal powder, no less than 40% silver, and no more than 50% base metal.

9. A method for preparing the conductive paste according to any one of claims 1-8, characterized in that, Includes the following steps: The conductive metal powder of the formula amount is premixed with the organic mixture to obtain a premix; The premix is ​​rolled to obtain the conductive slurry.

10. The preparation method according to claim 9, characterized in that, The premixing is carried out using a double planetary mixer, and the rolling is carried out using a three-roll mill.

11. A solar cell, characterized in that, The grid electrodes of the solar cell are formed by printing and sintering the conductive paste described in any one of claims 1-8.

12. The solar cell according to claim 11, characterized in that, The solar cell is a TOPCon cell, and its back side includes a passivated contact structure composed of an interface oxide layer and a doped polycrystalline silicon layer.

13. The solar cell according to claim 11 or 12, characterized in that, The grid line electrode includes a positive electrode grid located on the front side of the battery and / or a negative electrode grid located on the back side of the battery; The sintering temperature is 300-760℃; The grid electrodes are printed using either single-layer printing or double-layer printing, where a pure silver paste base layer is printed first, followed by the conductive paste.

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